Pager does not follow the request stack

Problem/Motivation

1. Some code calls PagerManager::createPager normally
2. Some time later a new request gets pushed on the request stack
3. Another call to PagerManager::createPager
4. The new request gets popped from the request stack
5. The pager now correlates with the already gone subrequest

Steps to reproduce

https://drupal.stackexchange.com/a/302336/69441

Proposed resolution

1. PagerParameters needs to be able to return the current request
2. PagerManager::createPager should use SplObjectStorage for the $pagers property where each request maps to the current page array

Remaining tasks

Agree, patch, test, commit.

User interface changes

None.

API changes

https://www.drupal.org/project/pagerer → breaks. I do not know how to handle that.

Data model changes

Release notes snippet